Catalysts, systems, and methods for the conversion of biomass to chemicals

ABSTRACT

The present disclosure relates to a composition that includes a solid support, a metal positioned on the solid support, and an oxide coating positioned to at least partially cover the metal. The compositions described herein may be utilized in methods that include contacting muconic acid and hydrogen to convert at least a portion of the muconic acid to adipic acid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/423,831 filed Nov. 18, 2016 and PCT application PCT/US2017/062157having an International Filing Date of Nov. 17, 2017, the contents ofboth of which are incorporated herein by reference in their entirety.

CONTRACTUAL ORIGIN

The United States Government has rights in this disclosure underContract No. DE-AC36-08GO28308 between the United States Department ofEnergy and the Alliance for Sustainable Energy, LLC, the Manager andOperator of the National Renewable Energy Laboratory.

BACKGROUND

Adipic acid is a major component of nylon-6,6 and is currently producedfrom the nitric acid oxidation of cyclohexanone. Adipic acid is producedin excess of 2,600 kta with a price of greater than $1.70 per kg. Due toits industrial importance, significant efforts are underway to produceadipic acid renewably. At the National Renewable Energy Laboratory(NREL), a hybrid biological and chemocatalytic process has beendeveloped to funnel both sugar and lignin-derived monomers into muconicacid as an intermediate for adipic acid production. Muconic acid can behydrogenated in the condensed phase over platinum group metals, with Pdbeing the most active. However, Pd is very susceptible to leaching intosolution. Platinum group metal (PGM) leaching can prohibit industrialscaling of catalytic processes due to the dramatic negative cost impact.Furthermore, although activated carbon catalyst supports have been shownto reduce leaching, they are highly susceptible to fouling from muconicacid. Thus, there remains a need for improved catalysts, systems, and/ormethods for converting biomass to useful fuels and/or chemicals, forexample, adipic acid.

SUMMARY

An aspect of the present disclosure is a composition that includes asolid support, a metal positioned on the solid support, and an oxidecoating positioned to at least partially cover the metal. In someembodiments of the present disclosure, the oxide may include at leastone of silica, titanium oxide, and/or alumina. In some embodiments ofthe present disclosure, the solid support may have a firstcharacteristic length between 1 micron and 10 mm. In some embodiments ofthe present disclosure, the metal may include at least one of ruthenium,rhodium, palladium, silver, osmium, iridium, platinum, and/or gold. Insome embodiments of the present disclosure, the metal may be present ata concentration between 0.1 wt % and 5.0 wt % relative to the metal andthe solid support. In some embodiments of the present disclosure, themetal may be in the form of a particle having a second characteristiclength of less than one micron.

In some embodiments of the present disclosure, the oxide coating mayinclude at least one of silica, alumina, titanium oxide, cerium oxide,magnesium oxide, tin oxide, and/or nickel oxide. In some embodiments ofthe present disclosure, the oxide coating may have a thickness between0.1 nm and 100 nm. In some embodiments of the present disclosure, theoxide coating may include at least one of a crack or a pore. In someembodiments of the present disclosure, the oxide coating may includebetween two oxide coatings and five oxide coatings. In some embodimentsof the present disclosure, the oxide coating may provide anaccessibility to the metal between 80% and 100% as measured by carbonmonoxide chemisorption. In some embodiments of the present disclosure,the composition may further include a surface area between 25 m²/g and200 m²/g as measured by nitrogen physisorption.

In some embodiments of the present disclosure, the composition mayfurther include a surface area between 25 m²/g and 200 m²/g as measuredby nitrogen physisorption, where the metal may include palladium, thesolid support may include at least one of titanium dioxide and/oralumina, the oxide coating may include between one oxide coating andfive oxide coatings of at least one of titanium dioxide or alumina, eachoxide coating may have a thickness between 1 nm and 5 nm, the metal mayhave an accessibility between 85% and 95% as measured by carbon monoxidechemisorption, the metal may be present at a concentration between 0.1wt % and 1 wt % relative to the metal and the solid support, and thesolid support may be in the form of a cylinder having a characteristiclength between 0.5 mm and 5 mm.

An aspect of the present disclosure is a method that includes contactingmuconic acid and hydrogen with a catalyst that includes a solid support,a metal positioned on the solid support, and an oxide coating positionedto at least partially cover the metal, where the contacting is performedwith the muconic acid in a liquid phase comprising an alcohol, and thecontacting converts at least a portion of the muconic acid to adipicacid. In some embodiments of the present disclosure, the alcohol mayinclude ethanol. In some embodiments of the present disclosure, thehydrogen may be supplied at a pressure between 1 atmosphere and 100atmosphere. In some embodiments of the present disclosure, thecontacting may be performed in a stirred tank reactor. In someembodiments of the present disclosure, the contacting may be performedat a temperature between 20° C. and 100° C. In some embodiments of thepresent disclosure, the contacting may be performed in a packed-bedreactor. In some embodiments of the present disclosure, the catalyst mayhave a characteristic length between about 0.5 mm and 5 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced figures of thedrawings. It is intended that the embodiments and figures disclosedherein are to be considered illustrative rather than limiting.

FIG. 1 illustrates muconic acid hydrogenation activity by PGMs on powderactivated carbon and silica supports in batch reactions (left panel),and PGM leaching after 35 minutes exposure to reaction conditions (rightpanel). Reaction conditions were as follows: 20 mL 1 wt % (of solution)muconic acid in ethanol, 24° C., 24 bar H₂, 15 mg catalyst, stirring1600 rpm. Batch reactions were performed in duplicate, with averagevalues reported. Turn over frequencies (TOF) for muconic acidhydrogenation were calculated based on pseudo-first order rate constantsfitted for duplicate reactions, by dividing the rate of muconic acidconsumption (molar basis) at 10% conversion by the moles ofsurface-exposed active metal determined by chemisorption. Metal leachingwas based on a single leaching measurement from combined solutions ofduplicate reactors.

FIG. 2 illustrates a hierarchical composite catalyst having a catalystsolid support with particles, in this case nanoparticles, that areover-coated with a coating, according to some embodiments of the presentdisclosure. The coating may adopt a porous nature that may enable masstransport to the nanoparticles but may also act to prevent agglomerationof the nanoparticles, dissolution of the nanoparticles, and/or otherdeleterious effects.

FIG. 3 illustrates a schematic of a catalyst architecture provided bysuccessive depositions that may produce catalysts having multiplecompositions and/or hierarchical coatings and/or layers that may servetailored catalyst purposes, according to some embodiments of the presentdisclosure.

FIG. 4 illustrates a method for converting bio-derived muconic acid andhydrogen to adipic acid using catalysts as described herein, accordingto some embodiments of the present disclosure.

FIG. 5 illustrates activity and leaching susceptibility for the freshuncoated catalyst and atomic layer deposition (ALD) Al₂O₃ overcoated 1wt % Pd/SiO₂ catalyst prepared in-house using a Sigma Aldrich SiO₂support, produced according to some embodiments of the presentdisclosure. Metal leaching was based on a single leaching measurementfrom combined solutions of duplicate reactors. Reaction conditions wereas follows: 20 mL 1 wt % muconic acid in ethanol, 24° C., 24 bar H₂, 15mg catalyst, stirring 1600 rpm.

FIG. 6 illustrates for the TiO₂ catalyst support obtained fromSaint-Gobain, a nitrogen physisorption isotherm profile, surface area,average pore volume (left), pore radius distribution, and average poreradius (right), according to some embodiments of the present disclosure.

FIG. 7 illustrates fouled catalyst activity for muconic acidhydrogenation with a commercial 1 wt % Pd on activated carbon (AC)catalyst from Alfa-Aesar (left) and 5-cycle Al₂O₃ ALD coated 1 wt %Pd/TiO₂ catalyst prepared in-house using a Saint-Gobain TiO₂ support(right), according to some embodiments of the present disclosure.

FIGS. 8A-8D illustrate catalyst activity and selectivity of the uncoatedand Al₂O₃ ALD coated 1% Pd/Al₂O₃Sigma Aldrich catalyst suite rangingfrom 1 to 10 ALD cycles, according to some embodiments of the presentdisclosure. Reaction conditions were as follows: 20 mL 1 wt % muconicacid in ethanol, 24° C., 24 bar H₂, 15 mg catalyst, stirring 1600 rpm.Pd leaching was measured after the reaction by filtering out thecatalyst and measuring the Pd content of the organic acid productmixture by ICP-MS. FIG. 8A for uncoated Pd/Al₂O₃;

FIG. 8B for 1-cycle (1 coating) of Al₂O₃ ALD on Pd/Al₂O₃; FIG. 8C for5-cycles (5 coatings) of Al₂O₃ ALD on Pd/Al₂O₃; and FIG. 8D for10-cycles (10 coatings) of Al₂O₃ ALD on Pd/Al₂O₃.

FIGS. 9A and 9B illustrate catalyst activity and selectivity of theuncoated (FIG. 9A) and 5-cycle Al₂O₃ ALD coated 1% Pd/TiO₂ catalystprepared in house using an Alfa Aesar TiO₂ support (FIG. 9B), accordingto some embodiments of the present disclosure. Reaction conditions wereas follows: 20 mL 1 wt % muconic acid in ethanol, 24° C., 24 bar H₂, 15mg catalyst, stirring 1600 rpm.

FIG. 10 illustrates SEM-EDX imaging (Panel A) and elemental mapping(Panels B and C) of the 5-cycle Al₂O₃ ALD coated 1% Pd/TiO₂ Alfa Aesarcatalyst.

FIGS. 11A and 11B illustrate catalyst activity and selectivity for theuncoated (FIG. 11A) and 5-cycle TiO₂ ALD overcoated 1% Pd/Al₂O₃SigmaAldrich catalyst (FIG. 11B), according to some embodiments of thepresent disclosure. Reaction conditions were as follows: 20 mL 1 wt %muconic acid in ethanol, 24° C., 24 bar H₂, 15 mg catalyst, stirring1600 rpm.

FIGS. 12A, 12B, and 12C illustrate catalyst activity and selectivity ofthe uncoated (FIG. 12A), 1-cycle (FIG. 12B), and 15-cycle Al₂O₃ ALDcoated 0.5% Pd/Al₂O₃ eggshell Alfa Aesar catalyst (FIG. 12C), accordingto some embodiments of the present disclosure. Reaction conditions wereas follows: 20 mL 1 wt % muconic acid in ethanol, 24° C., 24 bar H₂, 15mg catalyst, stirring 1600 rpm.

REFERENCE NUMBERS

-   -   100 . . . catalyst    -   110 . . . solid support    -   120 . . . particle    -   130 . . . coating    -   200 . . . method    -   210 . . . contacting    -   220 . . . muconic acid    -   230 . . . hydrogen (H₂)    -   240 . . . adipic acid

DETAILED DESCRIPTION

The present disclosure may address one or more of the problems anddeficiencies of the prior art discussed above. However, it iscontemplated that some embodiments as disclosed herein may prove usefulin addressing problems and deficiencies in a number of other technicalareas. Therefore, the embodiments described herein should notnecessarily be construed as limited to addressing any of the particularproblems or deficiencies discussed herein.

Muconic acid can be readily hydrogenated in the condensed phase overplatinum group metals (PGMs) at 70° C. and 30 bar, with Pd being themost active. However, as shown in FIG. 1, Pd is very susceptible toleaching into solution. Thus, aspects of the present disclosure relateto atomic layer deposition (ALD) for over-coating, as in the applicationof one or more coatings onto solid catalyst materials, for example e.g.noble metals, resulting in solid catalysts having improved stability.ALD is a form of chemical vapor deposition wherein layer-by-layer growthoccurs by self-limiting chemical reactions at a surface. The termself-limiting refers to the fact that the chemical precursors involvedin ALD react only with surface species and not with themselves. Thinoxide films may be deposited by iteratively exposing the surface to aset of precursors to complete an ALD ‘cycle’. Thus, in some embodimentsof the present disclosure, ALD may stabilize Pd metal sites againstleaching, while still allowing for accessibility to active metal sites.In addition, ALD overcoatings may be applied to a wide-range of solidsupport materials, e.g. oxides, that may be tuned to mitigate organicfouling observed with activated carbon supports.

As such, in some embodiments of the present disclosure, the use of ALDto deposit at least a one-layer coating onto palladium metal, e.g.nanocrystals, loaded at about 1 wt % on a solid support, e.g. TiO₂, aredescribed. The resistance of the resultant ALD coated catalysts toleaching of the palladium and to muconic acid organic fouling iscompared to a conventional commercial 1% Pd/AC (palladium on anactivated carbon support) catalyst. Both classes of catalyst wereinitially characterized and exposed to muconic acid in ethanol solutionsovernight to cause fouling of the catalysts by organic adsorption.Fouled catalysts were then screened to determine their catalyticactivity and susceptibility to leaching of the palladium in order toevaluate the benefits of ALD coatings for stabilizing muconic acidhydrogenation catalysts.

FIG. 2 illustrates a catalyst 100 that includes a solid support 110 witha plurality of particles 120 positioned on at least one surface of thesolid support 110, according to some embodiments of the presentdisclosure. Further, the plurality of particles 120 may be at leastpartially covered by a coating 130 such that the coating 130 may act asa protective layer, by preventing removal of the particles 120 from thecatalyst 100 and/or coalescence of the particles 120 into fewer and/orlarger particles (not shown). In some embodiments of the presentdisclosure, the particles 120 may provide catalytically active sitesthat promote a desired reaction; e.g. conversion of muconic acid toadipic acid. Thus, in some embodiments of the present disclosure, theparticles 120 may include at least one of a transition metal, and/or anoble metal (e.g. at least one of ruthenium, rhodium, palladium, silver,osmium, iridium, platinum, and/or gold.) Additional active metalmaterials can include bimetallic or trimetallic particles that arealloys, core-shells, or co-located particles, as well as interfacesbetween a catalyst active metal particle and the support material.

In some embodiments of the present disclosure a solid support 110 mayinclude at least one of a carbonaceous material (e.g. activated carbon)and/or an oxide (e.g. at least one of TiO₂, Al₂O₃, SiO₂, etc.). A solidporous support 110 may be in substantially spherical and/or cylindricalshape and/or any other suitable shape. The solid support 110 may be in arange of sizes including powders (<50 micron), granules (1 mm), pellets(>1 mm), and monoliths. Monolythic catalysts consist of an extraditedsolid material containing multiple parallel channels that may havecylinder diameters ranging from 10-150 mm, channel sizes ranging from1-100 mm², and lengths ranging from 10-1000 mm, which can be coated withcatalytically active species. The particles 120 may include any suitablematerial that provides sufficient activity, selectivity, and/or yield toconvert muconic acid and H₂ to adipic acid, and/or complete any otherreactions of choice. Thus, in some embodiments of the presentdisclosure, the particles 120 may include at least one noble metal, suchas platinum and/or palladium. The particles 120 may be deposited onto asurface of the solid support 110 by any suitable method, e.g. incipientwetness, ion exchange, strong electrostatic adsorption, nanoparticledispersion, chemical vapor deposition, and ALD. The particles 110 mayassume a shape such as spherical, cylindrical, cubic, octahedral,cuboidal/columnar, tetrahedral, and/or any other suitable shape. Theparticles 110 may be at least one of crystalline, polycrystalline,and/or amorphous. This includes a range of diameters that includeextremely disperse particles with a diameter <1 nm, highly disperseparticles with a diameter 1-10 nm, moderately dispersed particles with adiameter of 10-20 nm, and minimally dispersed particles with adiameter >20 nm. The final catalyst 100 may be in substantiallyspherical and/or cylindrical shape and/or any other suitable shape. Thefinal catalyst may be in a range of sizes including powders (<50micron), granules (1 mm), and pellets (>1 mm), or embedded monoliths.

FIG. 3 illustrates that, in some embodiments of the present disclosure,a catalyst 100 may include more than one particle and/or more than onecoating. In addition, a coating (e.g. 130A, 130B, and/or 130B) may beconstructed of more than one material, e.g. more than one oxide, byutilizing more than one precursor during the coating formation process(e.g. ALD). For example, FIG. 3 illustrates a catalyst 100 having threelayers of distinctly different particles (120A, 120B, and 120C) andcoatings (130A, 130B, and 130C). In this case, a first plurality ofparticles 120A is deposited onto a surface of a solid support 110 and afirst coating 130A is deposited such that substantially all of the firstparticles 120A are covered by the first coating 130A. In addition, asecond plurality of particles 120B are deposited onto the first coating130A and a second coating 130B is deposited such that substantially allof the second particles 120B are covered by the second coating 130B.Finally, a third plurality of particles 120C are deposited onto thesecond coating 130B and a third coating 130C is deposited such thatsubstantially all of the third particles 120C are covered by the thirdcoating 130C. As used herein, the term “substantially” refers to greaterthan 98%, greater than 99%, or up to 100%. As described herein, at leastone of the coatings (130A, 130B, and/or 130C) may be deposited by ALD.These coatings (130A, 130B, and/or 130C) may include at least one ofaluminum oxide (Al₂O₃), titanium oxide (TiO_(x)), cerium oxide (CeO₂),zirconium oxide (ZrO₂), silicon oxide (SiO₂), magnesium oxide (MgO), tinoxide (SnO₂), and/or nickel oxide (NiO). At least one of the particles(120A, 120B, and/or 120C) may be made of at least one of platinum,palladium, ruthenium, iridium, nickel, and/or rhodium. The coating 130thicknesses could range from less than one nanometer to five nanometersor more. The coatings (130A, 130B, and/or 130C) may adopt a form ofcomplete layers or partial layers that decorate specific targetedsurfaces of the catalyst (e.g. specific crystallographic facets) thecatalyst 100, the solid support 110, and/or the particles (120A, 120B,and/or 120C). Beyond improving catalyst stability, additionalfunctionality of at least one of the coatings (130A, 130B, and/or 130C)may include enhanced catalyst chemical activity and/or selectivity.Further, these coatings (130A, 130B, and/or 130C) may be deposited on avariety of solid supports including powders, spheres, granules, pellets,and/or monoliths.

In some embodiments of the present disclosure a coating on a catalyst,as described herein, may have at least one of a crack and/or pore on itssurface that may facilitate at least some mass transfer from thecatalyst's exterior environment to the particles that are at leastpartially covered by the coating. Differences in the amount and/or sizeof cracks and/or pores may be quantified by nitrogen physisorption andcarbon monoxide chemisorption as described herein. In some embodimentsof the present disclosure, a crack and/or pore may have a characteristiclength and/or diameter that is between 30% and 150% of thecharacteristic length of the particles (e.g. metal particles) of thecatalyst. In some embodiments of the present disclosure, thecharacteristic length of pores or widths of cracks may be smaller thanthe characteristic length of a particle, if the number of cracks orpores within close proximity to a particle (e.g. metal site) is greaterthan 2, 3, 4 or 5, where close proximity is defined by a characteristiclength scale of at most three times the diameter of a particular metalsite adhered to the support. The presence of pores and/or cracks on thecatalyst may be observed visually using high resolution imagingtechniques.

FIG. 4 illustrates a method 200 for converting muconic acid 220 andhydrogen 230 to adipic acid 240 by contacting 210 the muconic acid 220and hydrogen 230 with a solid catalyst having features as describedabove. This method can take place in the condensed phase, vapor phase,or any combination of the two. Reactor configurations may include batchor continuous flow systems such as a three-phase slurry reactor, stirredbatch reactor, loop reactor, or packed-bed reactor. Process conditionsmay range from 20-150° C. and with a hydrogen pressure from 1-100 bar.For the slurry reactor operation, this includes the use of fine catalystparticles (<100 micron) or granular catalyst particles (100 micron to 1mm), with muconic acid dissolved in a solvent (e.g., methanol, ethanol,tetrahydrofuran, acetone, acetic acid, ethyl acetate, γ-valerolactone,and/or other solvents in which muconic acid is soluble) from 1-50 wt %in solution, and the catalyst loaded into solution at 1-20 wt % ofsolution. The slurry reactor can operate with a residence time rangefrom 5 min to 300 min. For the packed bed reactor operation, thisincludes the use of fine catalyst particles (<100 micron), granularcatalyst particles (100 micron to 1 mm), or pellet catalyst particles(>1 mm) with muconic acid dissolved in solvent (e.g., methanol, ethanol,tetrahydrofuran, acetone, acetic acid, ethyl acetate, γ-valerolactone,and/or other solvents in which muconic acid is soluble). The muconicacid solution is fed to the reactor along with hydrogen gas flowing at ahydrogen to muconic acid molar ratio ranging 1:1 to 1:100. The packedbed reactor can operate with a weight hour space velocity (mass ofmuconic acid processed per mass of catalyst per hour) ranging from 0.05to 15

Catalyst Materials.

ALD experiments were conducted with a 1% Pd/SiO₂ catalyst (e.g.palladium particles deposited on a SiO₂ solid support) preparedin-house. A catalyst made of 1% Pd/SiO₂ was synthesized as describedpreviously (Green Chem. 18, 3397 (2016)). Blank Davisil Grade 633 highsurface area silica was obtained from Sigma Aldrich. This solid supportwas initially sieved >270 mesh (<53 micron) and calcined at 500° C. inair prior to loading with palladium. Palladium acetate (Sigma Aldrich)was used as the metal precursor and loaded by incipient wetness. Afterloading, the resultant catalyst, hereinafter referred to as “1% Pd/SiO₂Sigma Aldrich,” was dried at 110° C. and reduced in hydrogen flowing at200 standard cubic centimeters per minute (sccm) for 2 hours at 125° C.The catalyst was then coated by ALD with Al₂O₃ using the methodologydescribed below.

In some embodiments, ALD tests were performed with a 1% Pd/TiO₂ catalyst(e.g. palladium particles deposited on a TiO₂ solid support) preparedin-house. Blank pellet TiO₂ support was obtained from Saint-Gobain. Thesupport was ground and sieved to >270 mesh (<53 micron) prior to loadingwith palladium. Palladium was loaded onto the support by strongelectrostatic adsorption. Initially, about 1.98 g of the solid supportwas added to a beaker with ˜60 mL of deionized water. Due to the acidicsurface charge of the solid support, the pH of the solution was raisedto 11.5-12.0 using NaOH to deprotonate the solid support. In a separatebeaker, the target metal cationic precursor, tetraaminepalladium (II)chloride monohydrate, was added to ˜30 mL of DI water. Both solutionswere then combined and allowed to stir at 350 rpm for at least 2 hours.After stirring, the catalyst particles were vacuum filtered, dried, andreduced in 200 sccm of pure H₂ for about 4 hours at 150° C. ThePd-loaded catalyst hereinafter is referred to as “1% Pd/TiO₂Saint-Gobain.” The catalyst was then coated by ALD with Al₂O₃ using themethodology described below.

In some embodiments, ALD tests were performed with a 1% Pd/Al₂O₃catalyst (e.g. palladium particles deposited on Al₂O₃ solid support)obtained commercially in powder form (>50 mesh; <300 μm) from SigmaAldrich, hereinafter referred to as “1% Pd/Al₂O₃Sigma Aldrich”. Thecatalyst was then coated by ALD with Al₂O₃, as received, and separatelycoated by ALD with TiO₂, as received, using the methodology describedbelow.

In some embodiments, ALD tests were performed with a 0.7% Pd/TiO₂catalyst (e.g. palladium particles deposited on a TiO₂ solid support)prepared in-house. Blank pellet TiO₂ support was obtained Alfa Aesar.The support was ground and sieved to 30-50 mesh (300-600 micron) priorto loading with palladium. Palladium was loaded by strong electrostaticadsorption using pH adjustment with tetraaminepalladium (II) chloridemonohydrate. The catalyst was reduced at 150° C. under 200 sccm flowinghydrogen for 4 hours. The Pd-loaded catalyst is hereinafter referred toas “0.7% Pd/TiO₂ Alfa Aesar.” The catalyst was then coated by ALD withAl₂O₃ using the methodology described below.

In some embodiments, ALD tests were performed with an eggshell 0.5%Pd/Al₂O₃ catalyst (e.g. palladium particles deposited on an Al₂O₃ solidsupport) obtained commercially in 3.18-mm pellet form from Alfa Aesar,hereinafter referred to as “eggshell 0.5% Pd/Al₂O₃ pellets”. Thecatalyst was then coated by ALD with Al₂O₃, as received, using themethodology described below. For batch reactor testing, the uncoated andALD coated eggshell 0.5% Pd/Al₂O₃ pellet catalyst was ground and sievedto (>50 mesh; <300 micron) prior to use.

Atomic Layer Deposition.

Oxide-supported palladium catalysts were ALD overcoated using acustom-designed high surface area rotary ALD system. This ALD system isa viscous flow, hot-wall reactor outfitted with four mass flowcontrollers. The system contained a rotary drive shaft sample holderthat enabled physical agitation of granular materials in a tumbler withporous walls to allow precursor diffusion. The rotary ALD system wasalso equipped with four liquid sources, three heated sources, oxygen,nitrogen and hydrogen. The catalysts were coated by ALD as describedbelow:

1. Al₂O₃ coatings were deposited by ALD on the 1% Pd/SiO₂ Sigma Aldrichcatalyst. The stop flow ALD was performed in the rotary system operatedat 125° C. In stop-flow mode, the reactor is isolated from the pumpduring the exposure to the precursor. The pump is opened either afterthe exposure of the precursor, or after a defined exposure time. Theprecursors were trimethylaluminum (TMA) and water, both of which wereheld in vessels at room temperature. Three samples of ˜100 mg of 1%Pd/SiO₂ Sigma Aldrich catalyst were coated with 1, 5, and 15 cycles(corresponding to 1, 5, and 15 Al₂O₃ layers) of TMA/H₂O to depositaluminum oxide onto the 1% Pd/SiO₂. The timing sequences and carrier gas(99.9999% nitrogen) flows are summarized below in Table 1. Dose isdefined as the time that the precursor is introduced into the reactor.Exposure is defined as the time in which the precursor dwells inside thereactor after the dose. Purge if defined as the time to remove theprecursor from the reactor via flowing carrier gas. Evacuate is definedas the time to remove the precursor from the reactor with vacuum and noflowing carrier gas.

TABLE 1 TMA H₂O Expo- Evac- Expo- Evac- Dose sure Purge uate Dose surePurge uate Time (s) 60 300 300 0 60 300 300 0 MFC 1 60 60 60 60 60 60 6060 (sccm) MFC 2 20 20 20 20 20 20 20 20 MFC 3 20 20 20 20 20 20 20 20MFC 4 20 20 20 20 20 20 20 20

2. Al₂O₃ coatings were deposited by ALD on the 1% Pd/TiO₂ Saint-Gobaincatalyst. The 1% Pd/TiO₂ Saint-Gobain catalyst was coated by ALD with 5cycles of Al₂O₃ using TMA and H₂O under conditions identical to those inTable 1.

3. TiO₂ coatings were deposited by ALD on the 1% Pd/TiO₂ Saint-Gobaincatalyst. TiO₂ was deposited on the catalysts at 295° C. using titaniumisopropoxide (TTIP) and water. The TTIP was held at 75° C. and water atroom temperature. Three samples of 1, 5, 15 cycles were prepared,corresponding to 1, 5, and 15 layers of TiO₂ on the 1% Pd/TiO₂catalysts. Table 2 summarizes the timing and nitrogen carrier gas flows.

TABLE 2 TTIP H₂O Expo- Evac- Expo- Evac- Dose sure Purge uate Dose surePurge uate Time (s) 15 180 180 0 15 180 180 0 MFC 1 20 5 20 20 60 5 2020 (sccm) MFC 2 20 5 20 20 20 5 20 20 MFC 3 20 5 20 20 20 5 20 20 MFC 460 5 20 20 20 5 20 20

4. Al₂O₃ coatings were deposited by ALD on the 1% Pd/Al₂O₃Sigma-Aldrichcatalyst using an ALD fixed bed configuration. The catalyst was held inin a 1.5″×2″ stainless steel tray placed horizontally in the reactorwithout sample agitation. The Al₂O₃ precursors, TMA and H₂O, were heldat room temperature. The 1% Pd/Al₂O₃Sigma Aldrich catalyst was coated byALD with 1, 5, and 10 cycles of Al₂O₃ using stop-flow mode ALD at 200°C. with TMA and H₂O precursors, resulting in 1, 5, and 10 layers ofAl₂O₃ coatings deposited on the 1% Pd/Al₂O₃ catalysts. In stop-flowmode, one half cycle consists of dosing the sample with the precursor,exposure of the sample with the precursor isolated from the pump, apurge at higher flow rates, followed by evacuation of the chamber. Thesesteps were followed for both TMA and H₂O. One full cycle consists of twohalf cycles, the first with TMA and the second with H₂O. The timing andcarrier gas (99.9999% nitrogen) flow parameters for Al₂O₃ ALD areprovided below in Table 3.

TABLE 3 TMA H₂O Expo- Evac- Expo- Evac- Dose sure Purge uate Dose surePurge uate Time (s) 3 80 60 15 3 80 60 15 MFC 1 40 5 40 0 60 60 60 0(sccm) MFC 2 60 5 60 0 20 5 60 0 MFC 3 60 5 60 0 20 5 40 0 MFC 4 40 5 400 40 5 40 0

5. TiO₂ coatings were deposited by ALD on the 1% Pd/Al₂O₃Sigma Aldrichcatalyst. The 1% Pd/Al₂O₃Sigma Aldrich catalyst was coated by ALD withTiO₂ at 175° C. using the precursors TITIP and H₂O. The catalyst washeld in in a 1.5″×2″ stainless steel tray placed horizontally in thereactor without sample agitation. TITIP was held at 80° C. and H₂O atroom temperature. The process was operated in continuous-flow mode wherethere is no ‘exposure’ step. In continuous-flow mode, the carrier gasflow is constant and evacuation times are zero. The 1% Pd/Al₂O₃SigmaAldrich catalyst was coated by ALD with 5 cycles of TiO₂ using TITIP andH₂O in continuous-flow mode. Timing and carrier gas (99.9999% nitrogen)flow parameters for TiO₂ ALD are provided in Table 4.

TABLE 4 TTIP H₂O Expo- Evac- Expo- Evac- Dose sure Purge uate Dose surePurge uate Time (s) 100 0 300 0 100 0 600 0 MFC 1 40 40 40 40 40 40 4040 (sccm) MFC 2 60 60 60 60 60 60 60 60 MFC 3 20 20 20 20 20 20 20 20MFC 4 40 40 40 40 40 40 40 40

6. Al₂O₃ coatings were deposited by ALD on the 0.7% Pd/TiO₂ Alfa Aesarcatalyst. The 0.7% Pd/TiO₂ Alfa Aesar catalyst was coated by ALD with 5cycles of Al₂O₃ using TMA and H₂O under conditions identical to those inTable 3.

7. Al₂O₃ coatings were deposited by ALD on the eggshell 0.5% Pd/Al₂O₃pellet catalyst. The eggshell 0.5% Pd/Al₂O₃ pellet catalyst was coatedby ALD with 15 cycles of Al₂O₃ using TMA and H₂O under conditionsidentical to those in Table 3.

Catalyst Characterization:

The catalysts described above were characterized by various methods asdescribed below.

Nitrogen Physisorption.

Nitrogen physisorption was performed to measure the surface area ofcatalyst samples. The BET surface area and pore volume of the preparedcatalysts were measured with an ASAP 2020 using a 55-point nitrogenadsorption/desorption curve at −196° C. Prior to analysis, the samplewas degassed at 300° C. for five hours under vacuum. BET surface areaswere determined over a relative pressure range of 0.060 to 0.200 P/P₀.Pore size distributions were calculated using the BJH method off of theadsorption branch of the isotherms over a relative pressure range of0.140 to 0.995 P/P₀.

Elemental Analysis.

Inductively coupled plasma mass spectrometry (ICP-MS) was used tomeasure catalyst elemental composition and amount of leached Pd afterbatch and flow reactions. Initially, the amount of Pd leaching afterbatch reactor tests for the uncoated 1% Pd/SiO₂ Sigma Aldrich, Al₂O₃ ALDcoated 1% Pd/SiO₂ Sigma Aldrich, 1% Pd/AC, and Al₂O₃ ALD coated 1%Pd/TiO₂ Saint-Gobain catalysts was measured after filtering out thecatalyst and analyzing the combined ethanol and organic acid solution.For these catalyst materials, Pd leaching is reported as the percent(mass basis) of Pd leached into solution per Pd initially loaded intothe batch reactor as part of the catalyst. To improve the detectionlimit for Pd leaching with subsequent catalyst materials, (i.e., 1%Pd/Al₂O₃Sigma-Aldrich, 0.7% Pd/TiO₂ Alfa Aesar, eggshell 0.5% Pd/Al₂O₃pellet, including catalyst samples with and without ALD coatings), theethanol solution was evaporated and dried to concentrate leached Pd intothe solid organic acid fraction prior to ICP analysis. For thesecatalyst materials, Pd leaching is reported as the parts per million(mass basis) of Pd leached into the solid organic acid fractionprocessed in the batch or flow reactor.

Chemisorption.

Chemisorption was conducted to measure the amount of accessible surfacePd sites on catalyst samples. H₂ chemisorption measurements wereconducted using a Micromeritics Autochem II 2920 pulse analyzer. Priorto H₂ chemisorption analysis, catalysts samples (˜50-100 mg) weredegassed at 40° C. for 0.2 hours under Ar, dried at 100° C., reduced at280° C. in flowing 10% H₂/Ar (50 mL min⁻¹) for 1 hour, and purged at280° C. for 0.5 hours with Ar. When calculating turn over frequency, aPd:H stoichiometry of one-to-one was assumed. CO chemisorptionmeasurements were conducted using an Altamira AMI-390 micro-flow reactorsystem equipped with a thermal conductivity detector (TCD). Samples of˜50-100 mg were loaded in a quartz U-tube reactor and heated in 5% H₂/Arto 140° C. at 5° C. min⁻¹ with a hold time of 2 hours. After thereduction step, catalyst samples were flushed with helium at 50 mL min⁻¹for 1 hour to remove any weakly adsorbed hydrogen. The samples were thencooled to 30° C. and dosed with sequential 500 microliter pulses of 10%CO/He mixture. A 500-microliter sample loop was used to calibrate theTCD response for CO after each experiment. When calculating turn overfrequency, a Pd:CO stoichiometry of one-to-one was assumed.

SEM-EDS.

Scanning electron microscopy energy dispersive x-ray spectroscopy(SEM-EDS) was used to collect images and elemental maps of catalystsamples. SEM-EDS was performed on a FEI Quanta 400 FEG SEM under highvacuum equipped with an Everhart Thorney detector and an EDAX x-raydetector. Samples were mounted on aluminum stubs using conductive carbontape to reduce sample charging. Imaging and mapping was performed usingaccelerating voltages from 12.5 to 20 kV.

Catalyst Testing:

The catalysts described above were tested by various methods asdescribed below.

Catalyst Fouling Susceptibility.

To evaluate the resistance to organic fouling by adsorption, catalystswere exposed to ethanol solutions of muconic acid. Initially, 100 mg ofcatalyst was added to 30 g of a fully dissolved solution containing 1 wt% muconic acid in ethanol. The solutions were then stirred overnight andfiltered through a 0.2-micron filter and rinsed with 20 mL of ethanol.Filtrates were analyzed by ICP to determine the extent of initial metalleaching. The filtered and rinsed catalysts were then dried overnight at110° C. in air using an oven, prior to hydrogenation testing.

Muconic Acid Hydrogenation.

The activity of fresh and fouled catalysts was measured in a Parrmulti-batch reactor system in duplicate. For each test, 15 mg ofcatalyst was added to 20 g of solution containing 2 wt % muconic acid inethanol. The reactor was stirred at 1600 rpm and pressurized to 24 barof H₂. Periodic samples were collected using a syringe through a customreactor head sampling port. The samples were then filtered and analyzedby high-performance liquid chromatography (HPLC) to determine the extentof muconic acid conversion. After the reaction was complete, the reactorcontents were vacuum filtered (0.2-micron PES filter assembly, Nalgene)to remove catalyst particles, and subsequently the liquid filtrate wasanalyzed by ICP to examine the extent of palladium leaching from eachcatalyst.

Batch Reactor Testing.

Batch reactor testing was performed to measure changes in catalystactivity and leaching stability before and after ALD coating of thecatalysts by the methods described above. The reduction of muconic acidwas modeled as pseudo-first order to estimate the rate constant. Batchreactor catalyst hydrogenation productivity was calculated by dividingthe rate of muconic acid consumption (mass basis) at 10% conversion bythe total mass of catalyst loaded into the reactor. Catalyst TOF wascalculated by dividing the rate of muconic acid consumption (molarbasis) at 10% conversion by the moles of surface-exposed Pd determinedby chemisorption.

Continuous Flow Reactor Testing.

Continuous flow reactor testing was conducted with down-selectedcatalysts to measure changes in prolonged activity (>24 hours) andleaching stability before and after ALD coating of the catalysts by themethods described above. Testing was performed using a Parr tubularreactor system (Parr Instruments) operated in a down-flow trickle-bedconfiguration. The reactor system was outfitted with a HPLC pump (SeriesIII Scientific Instrument) to deliver liquid phase reactants, two massflow controllers (Brooks Instrument) to control inert gas and H₂ gasdelivery, tube-in-tube heat exchanger for cooling the reactor effluent,high-pressure 1-L stainless steel knockout pot with bottom samplingvalve, and a solenoid-controlled backpressure regulator (Tescom) tomaintain system pressure. Reactions were performed with gas and liquidreagents fed to through the top of a 32″ long, ¼″ inner-diameterstainless steel reaction tube surrounded by a clamshell furnace. Thetube temperature was monitored and controlled using an internalthermocouple centered in the catalyst bed and three furnace wallthermocouples. The tube was initially packed halfway with inert 1-mmglass beads (Sigma Aldrich) held in place with quartz wool (QuartzScientific Inc.). The catalyst bed was then loaded at the tubemid-height. Inert quartz sand (Quartz Scientific Inc.) sieved to fitthrough a 60-mesh opening (250 micron) and placed at the base and top ofthe catalyst packing to serve as a support. The remaining reactor tubevoid was then filled with inert glass beads and sealed with quartz wool.Continuous hydrogenation reactions were performed with H₂ supplied at200 sccm and a system pressure maintained at 500 psig. The mobile phaseconsisted of commercial cis,cis-muconic acid (Sigma Aldrich) dissolvedin 200-proof ethanol (muconic acid 8 g L⁻¹). Commercial succinic acid(Sigma Aldrich) was added as an internal standard (succinic acid 0.8 gL⁻¹). The mobile phase was delivered at a flow rate of 0.5 mL min⁻¹.Liquid effluent samples were collected from the knockout pot,syringe-filtered, and analyzed by HPLC. Subsamples of the liquidfiltrate were also filtered and the solvent was removed by blow-down toquantify leached Pd by ICP-MS. Flow reactor runs were conducted for atleast 24 hours. Flow reactor catalyst hydrogenation productivity wascalculated by dividing mass of muconic acid converted per hour per massof catalyst loaded into the reactor.

Results:

ALD oxide coatings mitigated palladium leaching during the hydrogenationof muconic acid. To provide a proof-of-concept demonstration for the useof ALD to mitigate palladium leaching with muconic acid hydrogenation,an initial suite of 1% Pd/SiO₂ catalysts with varying cycles of Al₂O₃ALD, resulting in corresponding numbers of Al₂O₃ ALD layers on thecatalysts, were synthesized and screened (see FIG. 5). For the non-ALDcoated catalyst using a SiO₂ solid support, the leaching of palladiumwas extensive with over 9% of the initial palladium loaded on thecatalyst leaching from the catalyst into solution. However, a palladiumon SiO₂ catalyst having a single layer of Al₂O₃ deposited by ALD ontothe palladium particles demonstrated no detectable leaching of thepalladium into solution by ICP. Catalysts with additional cycles of ALD(and, as a result, additional Al₂O₃ layers) further reduced the activityof the catalyst, with no detectable leaching of palladium into solutionby ICP. As described below, further ALD catalyst development wasconducted with a low surface area TiO₂ support.

Using a low surface area oxide catalyst support (<250 m² g⁻¹) may reduceorganic fouling during muconic acid hydrogenation and may result inimproved sustained catalytic activity. To evaluate the impact of thecatalyst support selection on the ability to resist fouling, acommercial 1% Pd/AC (e.g. palladium on an activated carbon solidsupport) catalyst was compared to a 5-cycle ALD Al₂O₃ coated 1% Pd/TiO₂catalyst. Previous characterization of the commercial 1% Pd/AC catalystconfirmed its high surface area (825 m² g⁻¹), and AC is a knownadsorbent for muconic acid which can lead to fouling of exposed metalsites. In contrast, the TiO₂ support showed a much lower surface area(155 m² g⁻¹), broad pore size distribution, and a high average poreradius of 70 Å (see FIG. 6).

Both palladium catalysts were then exposed overnight to a saturatedsolution of muconic acid to induce fouling of the catalysts by organicadsorption, with subsequent testing of the fouled catalysts' activitiesfor muconic acid hydrogenation. When normalized to an exposed surfacemetal site basis, fresh palladium catalysts displayed a muconic acidhydrogenation turn over frequency (TOF) ranging from 20-40 sec⁻¹,regardless of the support. With regards to hydrogenation productivity(normalized to the mass of muconic acid converted per mass of catalyst),the fresh 1% Pd/AC Alfa Aesar catalyst displayed a muconic acidhydrogenation productivity of 0.051 sec⁻¹. In contrast, the fouledcommercial 1% Pd/AC catalyst showed a dramatic reduction inhydrogenation productivity to 0.017 sec⁻¹, which is a drop of over 60%from the fresh catalyst performance (see Table 5 and FIG. 7). Inaddition, leaching was also significant with 0.8% of the loaded originalcatalyst palladium dissolving into solution. In comparison, the fouled1% Pd/TiO₂ Saint-Gobain catalyst having the 5-cycle Al₂O₃ ALD coatingshowed no significant drop in performance, with a hydrogenationproductivity of 0.161 sec⁻¹. Furthermore, leaching of palladium wasbelow in the 5-cycle Al₂O₃ ALD coated 1% Pd/TiO₂ Saint-Gobain catalyst,highlighting the benefit of using catalysts with ALD coatings and lowsurface area solid oxide supports for stabilizing muconic acidhydrogenation.

High fresh catalyst productivity was also observed with the 5-cycle TiO₂ALD coated 1% Pd/TiO₂ Saint-Gobain catalyst (see Table 5), althoughfollow-on stability testing was not performed.

TABLE 5 Batch Batch Batch Batch Pd Catalyst Fresh Fresh Fouled Leachingin Material TOF Productivity Productivity Solution Description (sec⁻¹)(sec⁻¹) (sec⁻¹) (%) Uncoated 20-40 0.051 0.017 0.8% of initial 1% Pd/ACPd metal Alfa Aesar 5-cycle ALD Al₂O₃ 20-40 >0.200 0.161 Below 1%Pd/TiO₂ detection limit Saint-Gobain 5-cycle ALD Not 0.110 Not Not TiO₂measured measured measured 1% Pd/TiO₂ Saint-Gobain

In some embodiments of the present disclosure, a coating may beconstructed with conformal coatings, defined as coatings that maintainthe surface morphology of the underlying material, with the inherentability to enable mass transport through porosity due to nanometer sizedcracking, reduced density, and/or incomplete coverage. Such coatings mayencapsulate or partially encapsulate system components including but notlimited to: dispersed particles down to the nanometer size rangesupported on the substrate, catalyst support materials, membranes,mesoporous materials, and other active layers. A coating may serve as apassive barrier to catalyst components and material diffusion,environmental barriers, membranes, and active catalytic components.Material types that may serve as coating include oxides, nitrides,sulfides, and/or pure elements. Examples of specific materials includebut are not limited to: aluminum oxide, zinc oxide, titanium oxide, ironoxide, zinc sulfide, tin oxide, platinum, palladium, ruthenium, andnickel. Other functional components of the composites include particles(sized down to the nanometer length scale), layers, partial layers, andpores formed by lost wax method may be fabricated with sequentialvapor-phase deposition. In some embodiments of the present disclosure,alternating deposition of coatings and particles, e.g. nanoparticles,directly formed by the deposition may produce concentric layers ofparticles encapsulated in the coating. Porosity in the coating describedwould enable mass transport to the dispersed nanoparticles. An examplewould be layers of aluminum oxide alternated with layers of discreteplatinum nanoparticles. FIG. 3 illustrates a schematic of a possiblecatalyst architecture obtained from sequential deposition includingmulti-metal particle layers and hierarchical coatings that serveadditional catalytic purposes. The primary vapor-phase synthesis methodis thermal ALD, which relies on the self-limiting reactions determinedby a temperature process window that enable layer-by-layer deposition.

In some embodiments of the present disclosure, vapor phase self-limingreactions at a material surface may be used to create and/or controlactive chemical sites through constructive and/or destructive processes.Principle strategies using ALD and/or atomic layer etching (ALE) may beutilized to achieve the desired results. ALD and ALE may use metalligand exchange processes to deposit and or etch out specific chemicalsites. These concepts may be applied to control active chemical sites.Some of these include but are not limited to Lewis acid/base sites,Brønsted acid/base sites, catalyst nanoparticles, etc. In someembodiments of the present disclosure, ALE may be used to removealuminum atoms from a preformed substrate or ALD material to create avacancy. The vacancy may remain for catalytic functionality or be filledvia ALD with a different atom. Another embodiment would be to first useALD to fabricate a material whereupon a single-layer deposition of theone material is performed, followed by subsequent ALD of a second,differing material. The second material may act as an embedded site forcatalytic function.

Tailoring ALD Cycle Number for Activity and Stability: The 1%Pd/Al₂O₃Sigma Aldrich catalyst was initially coated with a series of ALDcycles (1, 5, 10 cycles) using TMA and H₂O precursors to determine theinfluence of ALD cycle number on powder catalyst activity and leachingstability. The suite of ALD-coated catalysts was then characterized andtested, as shown in Table 6 and FIGS. 8A-8D. ICP-MS analysis confirmedthat the catalyst Al content increased with ALD cycle number, from 5.3to 24.2 wt % of additional Al, with weight percent based on the mass ofthe final catalyst including any ALD coating. Likewise, the Pd contentdecreased with increasing ALD cycle number, with Pd content defined aswt % of the total catalyst including the ALD coating. Physisorptionanalysis showed a range of surface areas that varied from 92 to 102 m²g⁻¹ for the uncoated and 1- to 5-cycle catalysts (uncoated 99 m² g⁻¹;1-cycle 102 m² g⁻¹; 5-cycle 92 m² g⁻¹). However, the 10-cycle ALDcatalyst showed a dramatic decrease in surface area to 66 m² g⁻¹. Withregards to Pd active site accessibility, the 1-cycle and 5-cycle ALDcatalysts retained 94% and 90% surface Pd accessibility compared to theuncoated catalyst, respectively, as indicated by CO chemisorption(uncoated 29.8 micromol g⁻¹; 1-cycle 27.9 micromol g⁻¹; 5-cycle 26.7micromol g⁻¹). However, the 10-cycle ALD catalyst retained only 6% Pdaccessibility (10-cycle 1.9 μmol g⁻¹). Both the CO chemisorption andphysisorption results indicate a nonlinear decrease in support surfacearea and Pd accessibility with increasing ALD cycle number in the rangeof 1 to 10 cycles for the 1% Pd/Al₂O₃Sigma Aldrich catalyst.

TABLE 6 Catalyst ICP-MS Surface CO Batch Batch Batch Pd Flow Flow PdMaterial Loading Area Uptake TOF Productivity Leaching ProductivityLeaching Description (wt %) (m² g⁻¹) (μmol g⁻¹) (sec⁻¹) (sec⁻¹) (ppm)(h⁻¹) (ppm) Uncoated Pd 1.00 99 29.8 39 0.164 2.8 6.50 1.95 1% Pd/Al₂O₃Sigma Aldrich 1-cycle Al₂O₃ Pd 0.80 102 27.9 24 0.095 2.4 Not Not 1%Pd/Al₂O₃ Al 5.3 measured measured Sigma Aldrich 5-cycle Al₂O₃ Pd 0.70 9226.7 29 0.110 1.3 4.50 0.84 1% Pd/Al₂O₃ Al 6.7 Sigma Aldrich 10-cycleAl₂O₃ Pd 0.55 66 1.90 42 0.011 <0.01 Not Not 1% Pd/Al₂O₃ Al 24.2measured measured Sigma Aldrich

The trend in Pd accessibility was further supported by batch reactorhydrogenation productivity tests with muconic acid. The 1-cycle and5-cycle ALD catalysts retained 58% and 68% of the batch reactorproductivity, respectively, compared to the uncoated catalyst (uncoated0.164 sec⁻¹; 1-cycle 0.095 sec⁻¹; 5-cycle 0.110 sec⁻¹), with no loss inadipic acid selectivity (see FIGS. 8A-8D). In contrast, the 10-cycle ALDcatalyst retained only 7% of the uncoated catalyst activity (10-cycle0.011 sec⁻¹). The Pd site TOF (mole of muconic acid converted per secper mole of catalyst surface Pd) fell within a range of 24 to 42 sec⁻¹for all catalysts. With regards to catalyst stability, batch reactor Pdleaching analysis determined that the 1-cycle and 5-cycle ALD catalystsreduced Pd leaching by 1.2-fold and 2.2-fold, respectively, compared tothe uncoated catalyst (uncoated 2.8 ppm; 1-cycle 2.4 ppm; 5-cycle 1.3ppm).

Based on the promising hydrogenation productivity and stability resultsfor the 5-cycle ALD catalyst, continuous testing was performed in atrickle-bed flow reactor. After 24 hours of time on stream, the 5-cyclecatalyst retained 69% of the continuous hydrogenation productivity (massof muconic acid converted per hour per mass of catalyst), compared tothe uncoated catalyst (uncoated 6.50 h⁻¹; 5-cycle 4.50 h⁻¹).Furthermore, the 5-cycle catalyst reduced Pd leaching by 2.3-fold(uncoated 1.95 ppm; 5-cycle 0.84 ppm).

Broad Applicability of Low Cycle ALD: To further evaluate theapplicability of low cycle ALD, a suite of Pd catalysts were preparedwith Al₂O₃ or TiO₂ ALD coating. The suite of uncoated Pd catalystsincluded the following: (a) 0.7% Pd/TiO₂ Alfa Aesar, (b) 1%Pd/Al₂O₃Sigma Aldrich, and (c) eggshell 0.5% Pd/Al₂O₃ pellets AlfaAesar.

The 0.7% Pd/TiO₂ Alfa Aesar granular catalyst was coated with 5 cyclesof Al₂O₃ ALD. As shown in Table 7 and FIGS. 9A and 9B, ALD coating thePd/TiO₂ catalyst resulted in an Al content of 2.5 wt % that decreasedthe surface area by 22% (uncoated 146 m² g⁻¹; 5-cycle 114 m² g⁻¹). Thecomparatively high decrease in surface area with the TiO₂ supportcompared to the Al₂O₃ support is likely associated with differences inthe physical and chemical properties of the substrates (e.g., porosity,hydroxyl density, reducibility). The 5-cycle Al₂O₃ ALD coated Pd/TiO₂catalyst retained 51% of the surface Pd accessibility compared to theuncoated catalyst, as determined by CO chemisorption (uncoated 34.7micromol g⁻¹; 5-cycle 17.6 micromol g⁻¹). Batch reactor testingdetermined that 31% of the catalyst hydrogenation productivity wasretained, (uncoated 0.094 sec⁻¹; 5-cycle 0.029 sec⁻¹), with no majorchange in adipic acid selectivity (FIGS. 9A and 9B). The intrinsic Pdactivity, determined by TOF measurements, fell within the range of 12 to19 sec⁻¹. ICP-MS analysis of the reactor filtrate confirmed a 3.2-foldreduction in Pd leaching with the 5-cycle Al₂O₃ ALD coated catalyst(uncoated 8.1 ppm; 5-cycle 2.5 ppm). Due to the differing elementalcomposition of the ALD coating and catalyst support, SEM-EDS was able toconfirm uniformly distributed Ti on the catalyst surface after ALDcoating (FIG. 10). Lastly, flow reactor testing determined that after 24hours of time on stream, the 5-cycle Al₂O₃ ALD coated catalyst retained75% of the continuous hydrogenation productivity (uncoated 0.81 h⁻¹;5-cycle 0.61 h⁻¹), with a 3.5-fold reduction in Pd leaching (uncoated2.25 ppm; 5-cycle 0.65 ppm).

TABLE 7 Catalyst ICP-MS Surface CO Batch Batch Batch Pd Flow Flow PdMaterial Loading Area Uptake TOF Productivity Leaching ProductivityLeaching Description (wt %) (m² g⁻¹) (μmol g⁻¹) (sec⁻¹) (sec⁻¹) (ppm)(h⁻¹) (ppm) Uncoated Pd 0.70 146 34.7 19 0.094 8.1 0.81 2.25 0.7%Pd/TiO₂ Alfa Aesar 5 cycle Al₂O₃ Pd 0.66 114 17.6 12 0.029 2.5 0.61 0.650.7% Pd/TiO₂ Al 2.5 Alfa Aesar

The 1% Pd/Al₂O₃ Sigma Aldrich powder catalyst was coated with 5 cyclesof TiO₂ ALD. As shown in Table 8 and FIGS. 11A and 11B, the TiO₂ ALDcoated 1% Pd/Al₂O₃ catalyst resulted in a Ti content of 4.0 wt %, withnegligible change in surface area (uncoated 99 m² g⁻¹; 5-cycle 102 m²g⁻¹). The 5-cycle TiO₂ ALD coated catalyst retained 94% of Pd activesite accessibility by CO chemisorption (uncoated 29.8 micromol g⁻¹;5-cycle 27.9 micromol⁻¹). Batch reactor testing determined that 78% ofthe catalyst hydrogenation productivity was retained, (uncoated 0.164sec⁻¹; 5-cycle 0.128 sec⁻¹), with no major change in adipic acidselectivity (FIGS. 11A and 11B). The intrinsic Pd activity, determinedby TOF measurements, fell within the range of 24 to 39 sec⁻¹. ICP-MSanalysis of the batch reactor filtrate confirmed a 2.2-fold reduction inPd leaching with the 5-cycle TiO₂ ALD coated catalyst (uncoated 2.8 ppm;5-cycle 1.3 ppm).

TABLE 8 ICP-MS Surface CO Batch Batch Batch Pd Catalyst Loading AreaUptake Rx TOF Productivity Leaching Description (wt %) (m² g⁻¹) (μmolg⁻¹) (sec⁻¹) (sec⁻¹) (ppm) Uncoated Pd 1.00 99 29.8 39 0.164 2.8 1%Pd/Al₂O₃ Sigma Aldrich 5-cycle TiO₂ Pd 0.93 108 18.3 49 0.128 1.3 1%Pd/Al₂O₃ Ti 3.1 Sigma Aldrich

The 0.5% Pd/Al₂O₃ pellet catalyst was coated with 1 and 15 cycles ofAl₂O₃ ALD. As shown in Table 9 and FIGS. 12A-12C, the Al₂O₃ ALD coated0.5% Pd/Al₂O₃ pellet catalyst resulted in an additional Al content of1.3 wt % and 9.66 wt % after 1 and 15 ALD cycles, respectively, with adecline in surface area with increasing ALD cycle number (uncoated 110m² g⁻¹; 1-cycle 107 m² g⁻¹; 15-cycle 93 m² g⁻¹). Batch reactor testingobserved no loss in catalyst hydrogenation productivity. The higheractivity observed with the Al₂O₃ ALD coated catalysts compared to theuncoated 0.5% Pd/Al₂O₃ pellet catalyst may be due to variability in theuncoated catalyst Pd content loaded into the reactor after grindingsieving the eggshell catalyst material. No major change in adipic acidselectivity was observed with the Al₂O₃ ALD coated catalysts (FIGS. 11Aand 11B). ICP-MS analysis of the batch reactor filtrate determined that15 ALD cycles were necessary for a 2-fold reduction in Pd leaching withthe pellet eggshell catalyst (uncoated 1.2 ppm; 1-cycle 0.8 ppm;15-cycle 0.6 ppm). The higher cycle number required for leachingreduction may be due to the larger physical dimensions of the pelletthat influence the ALD coating process, or differences in the chemicalproperties of the substrates (e.g., Pd site density, porosity, hydroxyldensity, reducibility).

TABLE 9 ICP-MS Surface Batch Batch Pd Catalyst Loading Area ProductivityLeaching Description (wt %) (m² g⁻¹) (sec⁻¹) (ppm) Uncoated eggshell Pd0.58 110 0.013 1.2 0.5% Pd/Al₂O₃ 1-cycle Al₂O₃ Pd 0.47 107 0.025 0.8eggshell 0.5% Pd/Al₂O₃ Al 1.3 15-cycle Al₂O₃ Pd 0.47 93 0.018 0.6eggshell 0.5% Pd/Al₂O₃ Al 9.66

EXAMPLES Example 1

A composition comprising: a solid support; a metal positioned on thesolid support; and an oxide coating positioned to at least partiallycover the metal.

Example 2

The composition of Example 1, wherein the solid support comprises atleast one of a carbonaceous material or an oxide.

Example 3

The composition of either Example 1 or 2, wherein the oxide comprises atleast one of silica, titanium oxide, or alumina.

Example 4

The composition of any one of Examples 1-3, wherein the carbonaceousmaterial comprises an activated carbon.

Example 5

The composition of any one of Examples 1-4, wherein the solid supporthas a shape comprising at least one of spherical, cylindrical, orgranular.

Example 6

The composition of any one of Examples 1-5, wherein the solid supporthas a first characteristic length between 1 micron and 10 mm.

Example 7

The composition of any one of Examples 1-6, wherein the firstcharacteristic length is between 50 microns and 5 mm.

Example 8

The composition of any one of Examples 1-7, wherein the metal comprisesa noble metal.

Example 9

The composition of any one of Examples 1-8, wherein the noble metalcomprises at least one of ruthenium, rhodium, palladium, silver, osmium,iridium, platinum, or gold.

Example 10

The composition of any one of Examples 1-9, wherein the noble metalcomprises palladium.

Example 11

The composition of any one of Examples 1-10, wherein the metal comprisesa transition metal.

Example 12

The composition of any one of Examples 1-11, wherein the metal ispresent at a concentration between 0.1 wt % and 5.0 wt % relative to themetal and the solid support.

Example 13

The composition of any one of Examples 1-12, wherein the concentrationis between 0.5 wt % and 1.0 wt %.

Example 14

The composition of any one of Examples 1-13, wherein the metal is in theform of a particle.

Example 15

The composition of any one of Examples 1-14, wherein the particle is inthe shape of at least one of spherical, cylindrical, or granular.

Example 16

The composition of any one of Examples 1-15, wherein the particle has asecond characteristic length of less than one micron.

Example 17

The composition of any one of Examples 1-16, wherein the secondcharacteristic length is between 1 nanometer and 100 nanometers.

Example 18

The composition of any one of Examples 1-17, wherein the particle is atleast one of crystalline, polycrystalline, or amorphous.

Example 19

The composition of any one of Examples 1-18, wherein the oxide coatingcovers substantially all of the metal.

Example 20

The composition of any one of Examples 1-19, wherein the oxide coatingcovers substantially all of the solid support.

Example 21

The composition of any one of Examples 1-20, wherein the oxide coatingcomprises at least one of silica, alumina, titanium oxide, cerium oxide,magnesium oxide, tin oxide, or nickel oxide.

Example 22

The composition of any one of Examples 1-21, wherein the oxide coatingcomprises at least one of silica, alumina, or titanium oxide.

Example 23

The composition of any one of Examples 1-22, wherein the oxide coatinghas a thickness between 0.1 nm and 100 nm.

Example 24

The composition of any one of Examples 1-23, wherein the thickness isbetween 1 nm and 5 nm.

Example 25

The composition of any one of Examples 1-24, wherein the oxide coatingcomprises at least one of a crack or a pore.

Example 26

The composition of any one of Examples 1-25, wherein the oxide coatingcomprises at least two oxide coatings.

Example 27

The composition of any one of Examples 1-26, wherein the oxide coatingcomprises between two oxide coatings and ten oxide coatings.

Example 28

The composition of any one of Examples 1-27, wherein the oxide coatingcomprises between two oxide coatings and five oxide coatings.

Example 29

The composition of any one of Examples 1-28, wherein each oxide coatinghas a thickness between 1 nm and 5 nm.

Example 30

The composition of any one of Examples 1-29, wherein the oxide coatingprovides an accessibility to the metal between 80% and 100% as measuredby carbon monoxide chemisorption.

Example 31

The composition of any one of Examples 1-30, wherein the accessibilityis between 85% and 95%.

Example 32

The composition of any one of Examples 1-31, further comprising: asecond metal positioned on the oxide coating; and a second oxide coatingpositioned to at least partially cover the second metal.

Example 33

The composition of any one of Examples 1-32, further comprising: a thirdmetal positioned on the second oxide coating; and a third oxide coatingpositioned to at least partially cover the third metal.

Example 34

The composition of any one of Examples 1-33, wherein at least one of thesecond metal and the third metal comprise at least one of a noble metalor a transition metal.

Example 35

The composition of any one of Examples 1-34, wherein at least one of thesecond oxide coating or the third oxide coating comprise at least one ofsilica, alumina, titanium oxide, cerium oxide, magnesium oxide, tinoxide, or nickel oxide.

Example 36

The composition of any one of Examples 1-35, further comprising asurface area between 25 m²/g and 200 m²/g as measured by nitrogenphysisorption.

Example 37

The composition of any one of Examples 1-36, wherein the surface area isbetween 65 m²/g and 110 m²/g.

Example 38

The composition of any one of Examples 1, further comprising: a surfacearea between 25 m²/g and 200 m²/g as measured by nitrogen physisorption,wherein: the metal comprises palladium, the solid support comprises atleast one of titanium dioxide or alumina, the oxide coating comprisesbetween one oxide coating and five oxide coatings of at least one oftitanium dioxide or alumina, each oxide coating has a thickness between1 nm and 5 nm, the metal has an accessibility between 85% and 95% asmeasured by carbon monoxide chemisorption, the metal is present at aconcentration between 0.1 wt % and 1 wt % relative to the metal and thesolid support, and the solid support is in the form of a cylinder havinga characteristic length between 0.5 mm and 5 mm.

Example 39

A method comprising: contacting muconic acid and hydrogen with acatalyst comprising: a solid support; a metal positioned on the solidsupport; and an oxide coating positioned to at least partially cover themetal, wherein: the contacting is performed with the muconic acid in aliquid phase comprising an alcohol, and the contacting converts at leasta portion of the muconic acid to adipic acid.

Example 40

The method of Example 39, wherein the contacting is performed at apressure of up to 24 bar.

Example 41

The method of either Example 39 or 40, wherein the alcohol comprisesethanol.

Example 42

The method of any one of Examples 39-41, wherein the hydrogen issupplied at a pressure between 1 atmosphere and 100 atmosphere.

Example 43

The method of any one of Examples 39-42, wherein the contacting isperformed in stirred tank reactor.

Example 44

The method of any one of Examples 39-43, wherein the contacting isperformed by mixing at least the liquid phase and the catalyst at aspeed of up to 1600 rpm.

Example 45

The method of any one of Examples 39-44, wherein the contacting isperformed at a temperature between 20° C. and 100° C.

Example 46

The method of any one of Examples 39-45, wherein the contacting isperformed in a packed-bed reactor.

Example 47

The method of any one of Examples 39-46, wherein the contacting isperformed at a pressure at an inlet to the packed-bed reactor of up to500 psig.

Example 48

The method of any one of Examples 39-47, wherein the catalyst has acharacteristic length between about 0.5 mm and 5 mm.

The foregoing discussion and examples have been presented for purposesof illustration and description. The foregoing is not intended to limitthe aspects, embodiments, or configurations to the form or formsdisclosed herein. In the foregoing Detailed Description, for example,various features of the aspects, embodiments, or configurations aregrouped together in one or more embodiments, configurations, or aspectsfor the purpose of streamlining the disclosure. The features of theaspects, embodiments, or configurations, may be combined in alternateaspects, embodiments, or configurations other than those discussedabove. This method of disclosure is not to be interpreted as reflectingan intention that the aspects, embodiments, or configurations requiremore features than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment, configuration, oraspect. While certain aspects of conventional technology have beendiscussed to facilitate disclosure of some embodiments of the presentinvention, the Applicants in no way disclaim these technical aspects,and it is contemplated that the claimed invention may encompass one ormore of the conventional technical aspects discussed herein. Thus, thefollowing claims are hereby incorporated into this Detailed Description,with each claim standing on its own as a separate aspect, embodiment, orconfiguration.

What is claimed is:
 1. A composition comprising: a solid support; ametal positioned on the solid support; and an oxide coating positionedto at least partially cover the metal; and wherein: the metal comprisespalladium, the solid support comprises at least one of titanium dioxideor alumina, the oxide coating comprises between one oxide coating andfive oxide coatings of at least one of titanium dioxide or alumina, eachoxide coating has a thickness between 1 nm and 5 nm, the metal has anaccessibility between 85% and 95% as measured by carbon monoxidechemisorption, the metal is present at a concentration between 0.1 wt %and 1 wt % relative to the metal and the solid support, and the solidsupport is in the form of a cylinder having a characteristic lengthbetween 0.5 mm and 5 mm and a surface area between 25 m²/g and 200 m²/gas measured by nitrogen physisorption.
 2. The composition of claim 1,wherein the solid support has a first characteristic length between 1micron and 10 mm.
 3. The composition of claim 1, wherein the metalcomprises at least one of ruthenium, rhodium, palladium, silver, osmium,iridium, platinum, or gold.
 4. The composition of claim 1, wherein themetal is present at a concentration between 0.1 wt % and 2.4% and at aconcentration between 2.6% and 5.0 wt % relative to the metal and thesolid support.
 5. The composition of claim 1, wherein the metal is inthe form of a particle having a second characteristic length of lessthan one micron.
 6. The composition of claim 1, wherein the oxidecoating comprises at least one of silica, titanium oxide, cerium oxide,magnesium oxide, tin oxide, or nickel oxide.
 7. The composition of claim1, wherein the oxide coating has a thickness between 0.4 nm and 100 nm.8. The composition of claim 1, wherein the oxide coating comprises atleast one of a crack or a pore.
 9. A method comprising: contactingmuconic acid and hydrogen with a catalyst comprising: a solid support; ametal positioned on the solid support; and an oxide coating positionedto at least partially cover the metal, wherein: the metal comprisespalladium, the solid support comprises at least one of titanium dioxideor alumina, the oxide coating comprises between one oxide coating andfive oxide coatings of at least one of titanium dioxide or alumina, eachoxide coating has a thickness between 1 nm and 5 nm, the metal has anaccessibility between 85% and 95% as measured by carbon monoxidechemisorption, the metal is present at a concentration between 0.1 wt %and 1 wt % relative to the metal and the solid support, and the solidsupport is in the form of a cylinder having a characteristic lengthbetween 0.5 mm and 5 mm and a surface area between 25 m²/g and 200 m²/gas measured by nitrogen physisorption, wherein: the contacting isperformed with the muconic acid in a liquid phase comprising an alcohol,and the contacting converts at least a portion of the muconic acid toadipic acid.
 10. The method of claim 9, wherein the alcohol comprisesethanol.
 11. The method of claim 9, wherein the hydrogen is supplied ata pressure between 1 atmosphere and 100 atmosphere.
 12. The method ofclaim 9, wherein the contacting is performed in a stirred tank reactor.13. The method of claim 9, wherein the contacting is performed at atemperature between 20° C. and 100° C.
 14. The method of claim 9,wherein the contacting is performed in a packed-bed reactor.